Thyroxine, Free (Free T4)

Overview:

The thyroid produces mostly T4, and almost all of it circulates bound to carrier proteins, leaving a small free fraction that can act on tissues. Measuring that free portion directly avoids the problem with total T4, which is affected by changes in carrier protein levels during pregnancy, with estrogen use and in some illnesses. Free T4 is usually measured after an abnormal TSH, to establish how far thyroid function has shifted and to distinguish patterns: low free T4 with high TSH indicates an underactive thyroid, while high free T4 with low TSH indicates an overactive one.

Categories:

Thyroid

Biomarkers:

1 biomarker